Her second service game let her down badly, even during the opening set, with only 40% of points won. Every time I get a second serve, I'm looking to attack.
A former world number one, Pliskova lost her round of 16 match against countrywoman, Karolina Muchova 6-4, 5-7, 11-13.
Barty captured the world number one ranking during her win at the lead-up event in Birmingham but the loss to Riske threatened to make her reign a short one.
In the post-match press conference, Barty remained a class act admitting it was her serve that ultimately cost her the match.
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"It's my desire to keep working hard to achieve my goals", said Barty, whose on-court style can be described as comfortable.
Barty, who returned rejuvenated to the sport after a spell playing cricket, said in stark contrast to her predecessor Japan's Naomi Osaka that being No 1 had not changed her or added pressure. Last month, she won her second professional tournament - the grass-court Rosmalen Championships in the Netherlands - and is 14-1 on grass this year.
Barty, though, was philosophical in defeat, reflecting instead on the most magnificent two months of her career. I'm really most proud about that.
"She never really (left the area) to train, like you see so numerous top players do", Bowman said.
Riske, who is due to get married after Wimbledon, did not seem to fall into that category when she said: "Bring it on!"
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She was spraying errors off her forehand - always the most likely wing to break down - but at least took the set to a tie-break. I went from, yeah, playing at the highest level of the sport to really struggling to do kind of day-to-day things.
On facing Serena Williams for a place in the last four, she said: "Bring it on!" She delivered 12 aces in the victory. Martic called for medical treatment on her left leg after the first game of the second set and her movement appeared to be hampered the rest of the way.
Barty will head to the U.S. hardcourt season with hope, having shrugged off a previously modest record at the Grand Slams with a first fourth-round appearance at the U.S. Open a year ago. Again, I'm ready for a war.
"The quarter-finals is fantastic but the way that I've been fighting, that is what is most exciting for me".
"I don't mediate I'll ever imagine it to be attractive", she acknowledged.
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Barty broke straight back when she unfurled a brilliant backhand victor down the line - a conventional two-hander this time rather than her one-handed slice - to make it 5-3 and the Aussie clinically served out the set.